Currently, the greatest infectious risk associated with blood transfusion is a septic reaction from bacterially contaminated blood products. In particular, platelets are very vulnerable to bacterial contamination since, after donation, they are typically kept at relatively warm temperatures that facilitate rapid bacterial growth. Approximately one in every 2000 platelet units are bacterially contaminated, and one in 50,000 bags result in a septic death. The risk of receiving a bacterially contaminated unit is currently higher than the risk of receiving a unit that is contaminated with a virus, such as HIV. Compounding this problem is that patients requiring platelet transfusion often have weakened immune systems, further increasing the risk of infection if contaminated platelets are introduced.
To deal with this problem, several European countries have adopted procedures for bacterial screening of platelets. Additionally, in the United States, the American Association of Blood Banks recently issued guidelines recommending that all platelet products be tested for bacteria.
To test the blood product contained in the blood product bag, it is often necessary to remove a small sample of the blood product from the blood product bag. This may be accomplished by attaching a syringe to the blood product bag. By manipulating the syringe, a measured sample of the blood product can then be drawn into the tube. This methodology has several drawbacks. The syringe inherently contains air, which may contaminate the sample or flow into the blood product bag and contaminate the blood product. Additionally, withdrawn sample contaminated by bacteria or other contaminants in the syringe may backflow back into the blood product bag, or be intentionally pushed back into the blood product bag if too much sample is initially withdrawn. Another disadvantage of the syringe is that it is awkward to manipulate.
Alternatively, a sample of the blood product may be removed from the blood product bag by connecting an evacuated, flexible sample bag to the blood product bag. Upon feeding the sample into the bag via gravity, the bag expands. In addition to allowing backflow back into the blood product bag, this methodology includes the drawback that it is difficult to acquire a precise amount of sample in the sample bag, since the bag does not consistently return to a predefined volume upon expanding.